Liquid-crystalline medium

ABSTRACT

The invention relates to a liquid-crystalline medium based on a mixture of polar compounds of positive dielectric anisotropy, characterised in that it comprises one or more compounds of the general formula I 
                         
in which R 1 ,
 
                         
L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , Z 1 , Z 2 , X, v and u are as defined in claim 1.

The present invention relates to a liquid-crystalline medium, to the use thereof for electro-optical purposes, and to displays containing this medium.

Liquid-crystals are used principally as dielectrics in display devices, since the optical properties of such substances can be modified by an applied voltage. Electro-optical devices based on liquid crystals are extremely well known to the person skilled in the art and can be based on various effects. Examples of such devices are cells having dynamic scattering, DAP (deformation of aligned phases) cells, guest/host cells, TN cells having a twisted nematic structure, STN (supertwisted nematic) cells, SBE (super-birefringence effect) cells and OMI (optical mode interference) cells. The commonest display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid-crystal materials must have good chemical and thermal stability and good stability to electric fields and electromagnetic radiation. Furthermore, the liquid-crystal materials should have low viscosity and produce short addressing times, low threshold voltages and high contrast in the cells.

They should furthermore have a suitable mesophase, for example a nematic or cholesteric mesophase for the above-mentioned cells, at the usual operating temperatures, i.e. in the broadest possible range above and below room temperature. Since liquid crystals are generally used as mixtures of a plurality of components, it is important that the components are readily miscible with one another. Further properties, such as the electrical conductivity, the dielectric anisotropy and the optical anisotropy, have to satisfy various requirements depending on the cell type and area of application. For example, materials for cells having a twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity.

For example, for matrix liquid-crystal displays with integrated non-linear elements for switching individual pixels (MLC displays), media having large positive dielectric anisotropy, broad nematic phases, relatively low birefringence, very high specific resistance, good UV and temperature stability and low vapour pressure are desired.

Matrix liquid-crystal displays of this type are known. Non-linear elements which can be used for individual switching of the individual pixels are, for example, active elements (i.e. transistors). The term “active matrix” is then used, where a distinction can be made between two types:

-   1. MOS (metal oxide semiconductor) or other diodes on a silicon     wafer as substrate. -   2. Thin-film transistors (TFTs) on a glass plate as substrate.

The use of single-crystal silicon as substrate material restricts the display size, since even modular assembly of various part-displays results in problems at the joins.

In the case of the more promising type 2, which is preferred, the electro-optical effect used is usually the TN effect. A distinction is made between two technologies: TFTs comprising compound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline or amorphous silicon.

The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counterelectrode on its inside. Compared with the size of the pixel electrode, the TFT is very small and has virtually no adverse effect on the image. This technology can also be extended to fully colour-capable displays, in which a mosaic of red, green and blue filters is arranged in such a way that a filter element is opposite each switchable pixel.

The TFT displays usually operate as TN cells with crossed polarisers in transmission and are illuminated from the back.

The term MLC displays here covers any matrix display with integrated non-linear elements, i.e., besides the active matrix, also displays with passive elements, such as varistors or diodes (MIM=metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications (for example pocket TVs) or for high-information displays for computer applications (laptops) and in automobile or aircraft construction. Besides problems regarding the angle dependence of the contrast and the response times, difficulties also arise in MLC displays due to insufficiently high specific resistance of the liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, September 1984: A 210–288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, September 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, p. 145 ff, Paris]. With decreasing resistance, the contrast of an MLC display deteriorates, and the problem of after-image elimination may occur. Since the specific resistance of the liquid-crystal mixture generally drops over the life of an MLC display owing to interaction with the interior surfaces of the display, a high (initial) resistance is very important in order to obtain acceptable service lives. In particular in the case of low-volt mixtures, it was hitherto impossible to achieve very high specific resistance values. It is furthermore important that the specific resistance exhibits the smallest possible increase with increasing temperature and after heating and/or UV exposure. The low-temperature properties of the mixtures from the prior art are also particularly disadvantageous. It is demanded that no crystallisation and/or smectic phases occur, even at low temperatures, and the temperature dependence of the viscosity is as low as possible. The MLC displays from the prior art thus do not meet today's requirements.

There thus continues to be a great demand for MLC displays having very high specific resistance at the same time as a large working-temperature range, short response times even at low temperatures and low threshold voltage which do not have these disadvantages, or only do so to a reduced extent.

In TN (Schadt-Helfrich) cells, media are desired which facilitate the following advantages in the cells:

-   -   extended nematic phase range (in particular down to low         temperatures)     -   the ability to switch at extremely low temperatures (outdoor         use, automobile, avionics)     -   increased resistance to UV radiation (longer service life).

The media available from the prior art do not allow these advantages to be achieved while simultaneously retaining the other parameters.

In the case of supertwisted (STN) cells, media are desired which enable greater multiplexability and/or lower threshold voltages and/or broader nematic phase ranges (in particular at low temperatures). To this end, a further widening of the available parameter latitude (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameters, elastic parameters) is urgently desired.

The invention has the object of providing media, in particular for MLC, TN or STN displays of this type, which do not have the above-mentioned disadvantages or only do so to a reduced extent, and preferably simultaneously have very high specific resistances and low threshold voltages. In particular, it is possible to use the compounds of the formula I for the preparation of low V_(th) mixtures which have a very good γ₁/clearing point ratio and relatively low Δn values. The mixtures according to the invention are particularly suitable for low Δn applications. The mixtures according to the invention are preferably used in reflective and transflective applications.

It has now been found that this object can be achieved if media according to the invention are used in displays.

The invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds of positive or negative dielectric anisotropy, characterised in that it comprises one or more compounds of the general formula I

in which

-   R¹ is an alkyl radical having from 1 to 12 carbon atoms which is     unsubstituted, monosubstituted by CN or CF₃ or at least     monosubstituted by halogen, where one or more CH₂ groups in these     radicals may also, in each case independently of one another, be     replaced by —O—, —S—,

—CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another,

-   L¹⁻⁶ are each, independently of one another, H or F, -   Z¹ and Z² are each, independently of one another, —CF₂CF₂— or a     single bond, where Z¹≠Z², -   X is F, Cl, CN, OCN, NCS, SCN, SF₅, an unsubstituted alkyl or alkoxy     radical, a halogenated alkyl radical, a halogenated alkenyl radical,     a halogenated alkoxy radical or a halogenated alkenyloxy radical     having up to 6 carbon atoms, and -   u is 0 or 1, and -   v is 0 or 1.

The compounds of the formula I have a broad range of applications. Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are predominantly composed; however, it is also possible to add compounds of the formula I to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or in order to optimise its threshold voltage and/or its viscosity.

In the pure state, the compounds of the formula I are colourless and form liquid-crystalline mesophases in a temperature range which is favourably located for electro-optical use. They are stable chemically, thermally and to light.

If R¹ is an alkyl radical and/or an alkoxy radical, this may be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexyloxy or heptyloxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, methoxy, octyloxy, nonyloxy, decyloxy or undecyloxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8-, or 9-oxadecyl.

If R¹ is an alkyl radical in which one CH₂ group has been replaced by —CH═CH—, this may be straight-chain or branched. It is preferably straight-chain and has from 2 to 10 carbon atoms. Accordingly, it is in particular vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, 4- or -5-enyl, hept-1-, -2-, -3-, 4-, -5- or -6-enyl, oct-1-, -2-, -3-, 4-, -5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, or dec--1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

If R¹ is an alkyl radical in which one CH₂ group has been replaced by —O— and one has been replaced by —CO—, these are preferably adjacent. These thus contain an acyloxy group —CO—O— or an oxycarbonyl group —O—CO. These are preferably straight-chain and have from 2 to 6 carbon atoms. Accordingly, they are in particular acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryl-oxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyi)ethyl, 3-(methoxycarbonyl)-propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

If R¹ is an alkyl radical in which one CH₂ group has been replaced by unsubstituted or substituted —CH═CH— and an adjacent CH₂ group has been replaced by CO or CO—O or O—CO, this may be straight-chain or branched. It is preferably straight-chain and has from 4 to 12 carbon atoms. Accordingly, it is in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryoyloxymethyl, 2-methacryloyloxyethyl, 3-meth-acryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.

If R¹ is an alkyl or alkenyl radical which is monosubstituted by CN or CF₃, this radical is preferably straight-chain. The substitution by CN or CF₃ is in any desired position.

If R¹ is an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain, and halogen is preferably F or Cl. In the case of polysubstitution, halogen is preferably F. The resultant radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituent may be in any desired position, but is preferably in the ω-position.

Compounds of the formula I which have wing groups R¹ which are suitable for polymerisation reactions are suitable for the preparation of liquid-crystalline polymers.

Compounds containing branched wing groups R¹ may occasionally be of importance owing to better solubility in the conventional liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components of ferroelectric materials.

Compounds of the formula I having S_(A) phases are suitable for thermally addressed displays.

Branched groups of this type generally contain not more than one chain branch. Preferred branched radicals R¹ are isopropyl, 2-butyl (=1-methyl-propyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methyl-butyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, iso-propoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methyl-pentoxy, 3-methylpentoxy, 2-ethylhexyloxy, 1-methylhexyloxy and 1-methylheptyloxy.

If R¹ is an alkyl radical in which two or more CH₂ groups have been replaced by —O— and/or —CO—O—, this may be straight-chain or branched. It is preferably branched and has from 3 to 12 carbon atoms. Accordingly, it is in particular biscarboxymethyl, 2,2-biscarboxyethyl, 3,3-biscarboxy-propyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycarbonyl)methyl, 2,2-bis(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl)propyl, 4,4-bis(methoxycarbonyl)butyl, 5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)hexyl, 7,7-bis(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)octyl, bis(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl or 5,5-bis(ethoxycarbonyl)hexyl.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for the said reactions. Use can also be made here of variants which are known per se, but are not mentioned here in greater detail.

The invention also relates to electro-optical displays (in particular STN or MLC displays having two plane-parallel outer plates, which, together with a frame, form a cell, integrated non-linear elements for switching individual pixels on the outer plates, and a nematic liquid-crystal mixture of positive dielectric anisotropy and high specific resistance which is located in the cell) which contain media of this type, and to the use of these media for electro-optical purposes. Besides for reflective displays, the mixtures according to the invention are also suitable for IPS (in plane switching) applications, OCB (optically controlled birefringence) applications and VA (vertical alignment) applications.

The liquid-crystal mixtures according to the invention enable a significant widening of the available parameter latitude.

The achievable combinations of clearing point, rotational viscosity γ₁ low Δn and dielectric anisotropy are far superior to previous materials from the prior art.

The requirement for a high clearing point, a nematic phase at low temperature and a high Δ∈ has hitherto only been achieved to an inadequate extent. Although mixtures such as, for example, MLC-6424 have a similar properties to the mixtures according to the invention, they have, however, significantly worse values for the rotational viscosity γ₁.

Other mixture systems have comparable flow viscosities ν₂₀ and Δ∈ values, but only have clearing points in the region of 60° C.

The liquid-crystal mixtures according to the invention, while retaining the nematic phase down to −20° C. and preferably down to −30° C., particularly preferably down to 40° C., enable clearing points above 80° C., preferably above 90° C., particularly preferably above 100° C., simultaneously dielectric anisotropy values Δ∈ of ≧6, preferably ≧8, and a high value for the specific resistance to be achieved, enabling excellent STN and MLC displays to be obtained. In particular, the mixtures are characterised by low operating voltages. The TN thresholds are below 2.0 V, preferably below 1.8 V, particularly preferably <1.7 V.

It goes without saying that, through a suitable choice of the components of the mixtures according to the invention, it is also possible for higher clearing points (for example above 110°) to be achieved at a higher threshold voltage or lower clearing points to be achieved at lower threshold voltages with retention of the other advantageous properties. At viscosities correspondingly increased only slightly, it is likewise possible to obtain mixtures having greater Δ∈ and thus lower thresholds. The MLC displays according to the invention preferably operate at the first Gooch and Tarry transmission minimum [C. H. Gooch and H. A. Tarry, Electron. Lett. 10, 2–4, 1974; C. H. Gooch and H. A. Tarry, Appl. Phys., Vol. 8, 1575–1584, 1975] are used, where, besides particularly favourable electro-optical properties, such as, for example, high steepness of the characteristic line and low angle dependence of the contrast (German Patent 30 22 818), a lower dielectric anisotropy is sufficient at the same threshold voltage as in an analogous display at the second minimum. This enables significantly higher specific resistances to be achieved using the mixtures according to the invention at the first minimum than in the case of mixtures comprising cyano compounds. Through a suitable choice of the individual components and their proportions by weight, the person skilled in the art is able to set the birefringence necessary for a pre-specified layer thickness of the MLC display using simple routine methods.

The flow viscosity ν₂₀ at 20° C. is preferably <60 mm²·s⁻¹, particularly preferably <150 mm²·s⁻¹. The rotational viscosity γ₁ of the mixtures according to the invention at 20° C. is preferably <180 mPa·s, particularly preferably <150 mPa·s. The nematic phase range is preferably at least 90°, in particular at least 100°. This range preferably extends at least from −20° to +80°.

Measurements of the capacity holding ratio (HR) [S. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5, 1381 (1989)] have shown that mixtures according to the invention comprising compounds of the formula I exhibit a significantly smaller decrease in the HR with increasing temperature than, for example, analogous mixtures comprising cyanophenylcyclohexanes of the formula

or esters of the formula

instead of the compounds of the formula I.

The UV stability of the mixtures according to the invention is also considerably better, i.e. they exhibit a significantly smaller decrease in the HR on exposure to UV.

The media according to the invention are preferably based on a plurality of (preferably two or more) compounds of the formula 1, i.e. the proportion of these compounds is 5–95%, preferably 10–60% and particularly preferably in the range 15–50%.

The individual compounds of the formulae I to XVIII and their sub-formulae which can be used in the media according to the invention are either known or they can be prepared analogously to the known compounds.

Preferred embodiments are indicated below:

-   -   Medium comprises one or more compounds of the formulae I1 to         I32:

-   -   X is preferably F, Cl, CN, OCN, NCS, SCN, SF₅, OCH₃, CH₃, OC₂H₅,         C₂H₅, OC₃H₇, C₃H₇, CF₃, CF₂H, OCF₃, OCF₂H, OCFHCF₃, OCFHCH₂F,         OCFHC₂HF, OCF₂CH₃, OCF₂CH₂F, OCF₂CHF₂, OCF₂CF₂CF₂H, OCF₂CF₂CH₂F,         OCFHCF₂CF₃, OCFHCF₂CHF₂, OCFHCFHCF₃, OCH₂CF₂CF₃, OCF₂CF₂CF₃,         OCF₂CFHCHF₂, OCF₂CH₂CHF₂, OCFHCF₂CHF₂, OCFHCFHCHF₂, OCFHCH₂CF₃,         OCH₂CFHCF₃, OCH₂CF₂CHF₂, OCF₂CFHCH₃, OCF₂CH₂CHF₂, OCFHCF₂CH₃,         OCFHCFHCHF₂, OCFHCH₂CF₃, OCH₂CF₂CHF₂, OCH₂CFHCHF₂, OCF₂CH₂CH₃,         OCFHCFHCH₃, OCFHCH₂CHF₂, OCH₂CF₂CH₃, OCH₂CFHCHF₂, OCH₂CH₂CHF₂,         OCHCH₂CH₃, OCH₂CFHCH₃, OCH₂CH₂CHF₂, OCClFCF₃, OCClFCClF₂,         OCClFCHF₂, OCFHCCl₂F, OCClFCHF₂, OCClFCClF₂, OCF₂CHCl₂,         OCF₂CHCl₂, OCF₂CCl₂F, OCF₂CClFH, OCF₂CClF₂, OCF₂CF₂CClF₂,         OCF₂CF₂CCl₂F, OCClFCF₂CF₃, OCClFCF₂CHF₂, OCClFCF₂CClF₂,         OCClFCFHCF₃, OCClFCClFCF₃, OCCl₂CF₂CF₃, OCClHCF₂CF₃,         OCClFCF₂CF₃, OCClFCClFCF₃, OCF₂CClFCHF₂, OCF₂CF₂CCl₂F,         OCF₂CCl₂CHF₂, OCF₂CH₂CClF₂, OCClFCF₂CFH₂, OCFHCF₂CCl₂F,         OCClFCFHCHF₂, OCClFCClFCF₂H, OCFHCFHCClF₂, OCClFCH₂CF₃,         OCFHCCl₂CF₃, OCCl₂CFHCF₃, OCH₂CClFCF₃, OCCl₂CF₂CF₂H,         OCH₂CF₂CClF₂, OCF₂CClFCH₃, OCF₂CFHCCl₂H, OCF₂CCl₂CFH₂,         OCF₂CH₂CCl₂F, OCClFCF₂CH₃, OCFHCF₂CCl₂H, OCClFCClFCHF₂,         OCFHCFHCCl₂F, OCClFCH₂CF₃, OCFHCCl₂CF₃, OCCl₂CF₂CFH₂,         OCH₂CF₂CCl₂F, OCCl₂CFHCF₂H, OCClHCClFCF₂H, OCF₂CClHCClH₂,         OCF₂CH₂CCl₂H, OCClFCFHCH₃, OCF₂CClFCC1₂H, OCClFCH₂CFH₂,         OCFHCC1₂CFH₂, OCCl₂CF₂CH₃, OCH₂CF₂CClH₂, OCCl₂CFHCFH₂,         OCH₂CClFCFCl₂, OCH₂CH₂CF₂H, OCClHCClHCF₂H, OCH₂CCl₂CF₂H,         OCClFCH₂CH₃, OCFHCH₂CCl₂H, OCClHCFHCClH₂, OCH₂CFHCCl₂H,         OCCl₂CH₂CF₂H, OCH₂CCl₂CF₂H, CH=CF₂, OCH=CF₂, CF═CF₂, OCF═CF₂,         CF═CHF, OCF═CHF, CH═CHF, OCH═CHF, CF₂CH₂CF₃, CF₂CHFCF₃ in         particular F, Cl, CN, CF₃, CHF₂, OCF₃, OCHF₂, OCFHCF₃, OCFHCHF₂,         OCFHCHF₂, OCF₂CH₃, OCF₂CHF₂, OCF₂CHF₂, OCF₂CF₂CHF₂, OCF₂CF₂CHF₂,         OCFHCF₂CF₃, OCFHCF₂CHF₂, OCF₂CF₂CF₃, OCF₂CF₂CClF₂, OCClFCF₂CF₃,         CH=CHF₂, OCH₃, OC₂H₅ or OC₃H₇.     -   Medium additionally comprises one or more compounds selected         from the group consisting of the general formulae II to VIII:

-   -    in which the individual radicals have the following meanings:

-   R₀: n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9     carbon atoms

-   X⁰: F, Cl, halogenated alkyl, alkenyl or alkoxy having from 1 to 6     carbon atoms,

-   Z⁰: —C₂H₄—, —CH₂O—, —COO—, —OCH₂—, —OCF₂—, —CF₂O—, —C₂F₄—, —CH₂CF₂—     or CF₂CH₂—,

-   Y¹, Y², Y³ and Y⁴: each, independently of one another, H or F,

-   r: 0 or 1

The compound of the formula IV is preferably

The medium additionally comprises one or more dioxanes of the formulae D1 to D4:

in which R⁰ is as defined above.

-   -   The medium additionally comprises one or more compounds selected         from the group consisting of the general formulae IX to XVIII:

-   -    in which R⁰, X⁰, Y¹ and Y² are each, independently of one         another, as defined in claim 2. X⁰ is preferably F, Cl, CF₃,         OCF₃ or OCHF₂. R⁰ is preferably alkyl, oxaalkyl, fluoroalkyl or         alkenyl, each having up to 6 carbon atoms.     -   The medium additionally comprises one or more compounds having         fused rings, of the formulae A-1 to A-6:

-   -    in which R⁰ is as defined in claim 2.     -   The proportion of the compounds of the formulae A-1 to A-6 is         0–20% by weight, preferably 3–15% by weight, in particular 3–10%         by weight;     -   The proportion of compounds of the formulae I to VIII together         in the mixture as a whole is at least 30% by weight, preferably         at least 50% by weight;     -   The proportion of compounds of the formula I in the mixture as a         whole is from 1 to 50% by weight, preferably 2–30% by weight and         in particular 5–25% by weight;     -   The proportion of compounds of the formulae II to VIII in the         mixture as a whole is from 20 to 80% by weight;

-   -   The medium comprises one or more compounds of the formulae II,         III, IV, V, VI, VII or VIII;     -   R⁰ is straight-chain alkyl or alkenyl having from 2 to 7 carbon         atoms;     -   The medium essentially consists of compounds of the formulae I         to VIII;     -   The medium preferably comprises one, two or three compounds of         the formula I;     -   The medium comprises a mixture of compounds of the formula I in         which R¹ is methyl, ethyl, n-C₃H₇, n-C₄H₉, n-C₅H₁₁ or n-C₆H₁₁;     -   The medium comprises further compounds, preferably selected from         the following group consisting of the general formulae XIX to         XXII:

-   -    in which R⁰, X⁰, Y¹, Y² and Y³ are as defined above, and the         1.4-phenylene rings may be substituted by methyl, CN, chlorine         or fluorine. The 1.4-phenylene rings are preferably         monosubstituted or polysubstituted by fluorine atoms.     -   The medium preferably comprises two-ring carbocyclic compounds         of the formula XXIII

-   -    where

and are each, independently of one another,

-   Z⁰ is a single bond, —C₂H₄—, —C₄H₈—, —COO—, —O—CO—, —CF₂O— or     —OCF₂—, -   r⁰ is 1 or 2, -   R^(0′)is as defined for R⁰, and -   X^(0″) is OCF₃, F, Cl, CF₃, alkyl or alkoxy.

Preferred sub-formulae of the formula XXIII are

Very particularly preferred sub-formulae of the formula XXIII are

where alkyl is a straight-chain alkyl radical having 1–8 carbon atoms, in particular having 2–5 carbon atoms.

The medium preferably comprises two or three compounds of the formula XXIII.

-   -   The proportion of the compounds of the formula XXIII in the         medium according to the invention is 5–40% by weight, in         particular 5–35% by weight.     -   The I: (II+III+IV+V+VI+VII+VIII) weight ratio is preferably from         1:10 to 10:1.     -   The medium essentially consists of compounds selected from the         group consisting of the general formulae I to XVIII.

The term “alkyl” covers straight-chain and branched alkyl groups having 1–7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2–5 carbon atoms are generally preferred.

The term “alkenyl” covers straight-chain and branched alkenyl groups having 2–7 carbon atoms, in particular the straight-chain groups. Particular alkenyl groups are C₂–C₇-1E-alkenyl, C₄–C₇-3E-alkenyl, C₅–C₇-4-alkenyl, C₆–C₇-5-alkenyl and C₇-6-alkenyl, in particular C₂–C₇-1E-alkenyl, C₄–C₇-3E-alkenyl and C₅–C₇-4-alkenyl. Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally preferred.

The term “fluoroalkyl” preferably covers straight-chain groups having a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.

The term “oxaalkyl” preferably covers straight-chain radicals of the formula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and m are each, independently of one another, from 1 to 6. n is preferably=1 and m is preferably from 1 to 6.

It has been found that even a relatively small proportion of compounds of the formula I mixed with conventional liquid-crystal materials, but in particular with one or more compounds of the formulae II, III, IV, V, VI, VII and/or VIII, results in a significant lowering of the threshold voltage and in low birefringence values, with broad nematic phases with low smectic-nematic transition temperatures being observed at the same time, improving the shelf life. Particular preference is given to mixtures which, besides one or more compounds of the formula I, comprise one or more compounds of the formula IV, in particular compounds of the formula IVa in which X⁰ is F, OCHF₂ or OCF₃. The compounds of the formulae I to VIII are colourless, stable and readily miscible with one another and with other liquid-crystalline materials. Furthermore, the mixtures according to the invention are distinguished by very high clearing points, the values for the rotational viscosity γ₁ being comparatively low.

Through a suitable choice of the meanings of R⁰ and X⁰, the addressing times, the threshold voltage, the steepness of the transmission characteristic lines, etc., can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like generally result in shorter addressing times, improved nematic tendencies and a higher ratio of the elastic constants k₃₃ (bend) and k₁₁ (splay) compared with alkyl or alkoxy radicals. 4-alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller values of k₃₃/k₁₁ compared with alkyl and alkoxy radicals.

A —CH₂CH₂— group generally results in higher values of k₃₃/k₁₁ compared with a single covalent bond. Higher values of k₃₃/k₁₁ facilitate, for example, flatter transmission characteristic lines in TN cells with a 90° twist (in order to achieve grey shades) and steeper transmission characteristic lines in STN, SBE and OMI cells (greater multiplexability), and vice versa.

The optimum mixing ratio of the compounds of the formulae I and II+III+IV+V+VI+VII+VIII depends substantially on the desired properties, on the choice of the components of the formulae I, II, III, IV, V, VI, VII and/or VIII, and the choice of any other components that may be present.

Suitable mixing ratios within the range given above can easily be determined from case to case.

The total amount of compounds of the formulae I to XVIII in the mixtures according to the invention is not crucial. The mixtures can therefore comprise one or more further components for the purposes of optimising various properties. However, the observed effect on the addressing times and the threshold voltage is generally greater, the higher the total concentration of compounds of the formulae I to XVIII.

In a particularly preferred embodiment, the media according to the invention comprise compounds of the formulae II to VIII (preferably II, III and/or IV, in particular IVa) in which X⁰ is F, OCF₃, OCHF₂, OCH═CF₂, OCF═CF₂ or OCF₂—CF₂H. A favourable synergistic effect with the compounds of the formula I results in particularly advantageous properties. In particular, mixtures comprising compounds of the formula I and of the formula IVa are distinguished by their low threshold voltages.

The construction of the MLC display according to the invention from polarisers, electrode base plates and surface-treated electrodes corresponds to the conventional construction for displays of this type. The term “conventional construction” is broadly drawn here and also covers all derivatives and modifications of the MLC display, in particular including matrix display elements based on poly-Si TFT or MIM.

A significant difference between the displays according to the invention and the conventional displays based on the twisted nematic cell consists, however, in the choice of the liquid-crystal parameters of the liquid-crystal layer.

The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner conventional per se. In general, the desired amount of the components used in the lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing.

The dielectrics may also comprise further additives known to the person skilled in the art and described in the literature. For example, 0–15% of pleochroic dyes or chiral dopants can be added.

C denotes a crystalline phase, S a smectic phase, S_(C) a smectic C phase, N a nematic phase and I the isotropic phase.

V₁₀ denotes the voltage for 10% transmission (viewing angle perpendicular to the plate surface). t_(on) denotes the switch-on time and t_(off) the switch-off time at an operating voltage corresponding to 2 times the value of V₁₀. Δn denotes the optical anisotropy and no the refractive index. Δ∈ denotes the dielectric anisotropy (Δ∈=∈_(∥)−∈_(⊥), where ∈_(∥) denotes the dielectric constant parallel to the longitudinal molecular axes and ∈_(⊥) denotes the dielectric constant perpendicular thereto). The electro-optical data were measured in a TN cell at the 1st minimum (i.e. at a d·Δn value of 0.5) at 20° C., unless expressly stated otherwise. The optical data were measured at 20° C., unless expressly stated otherwise.

In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by means of acronyms, the transformation into chemical formulae taking place in accordance with Tables A and B below. All radicals C_(n)H_(2n+1) and C_(m)H_(2m+1) are straight-chain alkyl radicals having n and m carbon atoms respectively; n and m are preferably 0, 1, 2, 3, 4, 5, 6 or 7. The coding in Table B is self-evident. In Table A, only the acronym for the parent structure is indicated. In individual cases, the acronym for the parent structure is followed, separated by a dash, by a code for the substituents R¹, R², L¹ and L²:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H H nOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) H H n C_(n)H_(2n+1) CN H H nN.F C_(n)H_(2n+1) CN H F nF C_(n)H_(2n+1) F H H nOF OC_(n)H_(2n+1) F H H nCl C_(n)H_(2n+1) Cl H H nF.F C_(n)H_(2n+1) F H F nF.F.F C_(n)H_(2n+1) F F F nCF₃ C_(n)H_(2n+1) CF₃ H H nOCF₃ C_(n)H_(2n+1) OCF₃ H H nOCF₂ C_(n)H_(2n+1) OCHF₂ H H nS C_(n)H_(2n+1) NCS H H rVsN C_(r)H_(2r+1)—CH═CH— CN H H C_(s)H_(2s)— rEsN C_(r)H_(2r+1)—O—C_(s)H_(2s)— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) H H nOCCF₂.F.F C_(n)H_(2n+1) OCH₂CF₂H F F V-n CH₂═CH C_(n)H_(2n+1) H H

Preferred mixture components of the mixture concept according to the invention are given in Tables A and B.

TABLE A

PYP PYRP

BCH CBC

CCH CCP

CPTP

CEPTP

ECCP CECP

CCEEP CEECP

EPCH PCH

PTP BECH

EBCH CPC

B FET-nF

CGG CGU

CFU

TABLE B

BCH-n.Fm

CFU-n-F

Inm

CBC-nmF

PDX-n

CCZU-n-F

K3n

ECCP-nm

ECCP-nF.F.F

CCH-n1EM

T-nFm

CGU-n-F

CDU-n-X

CGG-n-F

CWC-n-m

CCH-nCF₃

CUP-nF.F

CC-n-V

CWCC-n-m

PQU-n-F

CCG-n-OT

CCU-n-OT

CCQU-n-F

CCQG-n-OT

Dec-U-n-F

CPTU-n-F

GPTU-n-F

PGU-n-F

CC-n-V1

CCP-V-1

CGZP-n-OT

CCP-nF.F

Nap-U-n-F

CPZU-n-F

CWC-n-m

CC-n-DDT

CC-n-OMT

DU-n-N

CWCU-n-F

CWCG-n-F

CWCG-n-OT

CCOC-n-m

CCWU-n-F

TABLE C Table C shows possible dopants which are generally added to the compounds according to the invention.

C 15

CB 15

CM 21

R/S-811

CM 44

CM 45

CM 47

R/S-1011

R/S-3011

CN

R/S-8950

R/S-2011

Besides one or more compounds of the formula I, particularly preferred mixtures comprise one, two, three, four, five or more compounds from Table B.

The following examples are intended to explain the invention without restricting it. Above and below, percentages are percent by weight. All temperatures are given in degrees Celsius. m.p. denotes melting point, cl.p. =clearing point. Furthermore, C=crystalline state, N=nematic phase, S=smectic phase and I=isotropic phase. The data between these symbols represent the transition temperatures. An denotes optical anisotropy (589 nm, 20° C.). The flow viscosity ν₂₀ (mm²/sec) and the rotational viscosity γ₁ [mPa·s] were each determined at 20° C.

MIXTURE EXAMPLES Example M1

PCH-7-F 4.00% S → N [° C.]: <−40 CC-5-V 12.00% Clearing point [° C.]: 92.5 CCP-2F.F.F 12.00% Δn [589 nm, 20° C.]: +0.0864 CCP-3F.F.F 11.00% γ₁ [mPa · s, 20° C.]: 130 CCP-5F.F.F 7.00% V₁₀ [V]: 1.76 CWCG-3-F 8.00% d · Δn [μm, 20° C.]: 0.50 CCP-20CF₃ 8.00% Twist [°]: 90 CCP-30CF₃ 8.00% CCP-40CF₃ 6.00% CCP-50CF₃ 8.00% BCH-2F.F 8.00% BCH-3F.F 8.00%

Example M2

CCH-3CF₃ 8.00% S → N [° C.]: <−40 CCH-5CF₃ 8.00% Clearing point [° C.]: 83.5 CCP-2F.F.F 11.00% Δn [589 nm, 20° C.]: +0.0702 CCP-3F.F.F 12.00% γ₁ [mPa · s, 20° C.]: 138 CCP-5F.F.F 5.00% Twist [°]: 90 CCZU-2-F 4.00% V₁₀ [V]: 1.37 CCZU-3-F 15.00% d · Δn [μm, 20° C.]: 0.50 CCZU-5-F 4.00% CCP-20CF₃.F 7.00% CCP-30CF₃.F 7.00% CCP-50CF₃.F 3.00% CWCU-3-F 16.00%

Example M 3

BCH-3F.F 10.80% Clearing point [° C.]: 98.5 BCH-5F.F 9.00% Δn [589 nm, 20° C.]: +0.0960 ECCP-30CF₃ 4.50% Δε [1 KHz, 20° C.]: +5.4 ECCP-50CF₃ 4.50% CBC-33F 1.80% CBC-53F 1.80% CBC-55F 1.80% PCH-6F 7.20% PCH-7F 5.40% CCP-20CF₃ 7.20% CCP-30CF₃ 10.80% CCP-40CF₃ 6.30% CCP-50CF₃ 9.90% PCH-5F 9.00% CWCG-3-F 9.97%

Example M 4

BCH-3F.F 10.80% BCH-5F.F 9.00% ECCP-30CF₃ 4.50% ECCP-50CF₃ 4.50% CBC-33F 1.80% CBC-53F 1.80% CBC-55F 1.80% PCH-6F 7.20% PCH-7F 5.40% CCP-20CF₃ 7.20% CCP-30CF₃ 10.80% CCP-40CF₃ 6.30% CCP-50CF₃ 9.90% PCH-5F 9.00% CWCG-3-F 10.02%

Example M 5

BCH-3F.F 9.60% BCH-5F.F 8.00% ECCP-30CF₃ 4.00% ECCP-50CF₃ 4.00% CBC-33F 1.60% CBC-53F 1.60% CBC-55F 1.60% PCH-6F 6.40% PCH-7F 4.80% CCP-20CF₃ 6.40% CCP-30CF₃ 9.60% CCP-40CF₃ 5.60% CCP-50CF₃ 8.80% PCH-5F 8.00% CWCG-3-F 19.97%

Example M 6

CCH-301 13.00% CCH-501 15.00% CCP-2F.F.F 8.00% CCP-3F.F.F 0.00% CCZU-2-F 4.00% CCZU-3-F 13.00% CCZU-5-F 4.00% CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 2.00% CH-35 2.00% CH-43 3.00% CH-45 3.00% CWC-5-3 5.00% CWCU-3-F 15.00%

6.00%

Example M 7

CCH-301 14.00% CCH-501 13.00% CCP-2F.F.F 5.00% CCZU-2-F 4.00% CCZU-3-F 8.00% CCZU-5-F 4.00% CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 2.00% CCPC-35 2.00% CH-35 2.00% CH-43 3.00% CH-45 2.00% CCQU-3-F 5.00% CWC-5-3 5.00% CWCU-3-F 8.00% CECU-3-F 5.00% ECCP-3F.F.F 5.00%

6.00%

Example M 8

CCP-2F.F.F 9.00% CCP-3F.F.F 9.00% CCP-5F.F.F 4.00% CCZU-2-F 4.00% CCZU-3-F 14.00% CCZU-5-F 4.00% CCP-20CF₃.F 4.00% CCP-30CF₃.F 4.00% CCP-50CF₃.F 4.00% CGU-2-F 3.00% CGU-3-F 2.00% CCH-3CF₃ 5.00% CCH-5CF₃ 5.00% CCQU-2-F 10.00% CCQU-3-F 10.00% CWCU-3-F 5.00%

4.00%

Example 9

CCP-2F.F.F 11.00% CCP-3F.F.F 10.00% CCP-5F.F.F 4.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CCP-20CF₃.F 7.00% CCP-30CF₃.F 4.00% CCP-50CF₃.F 4.00% CGU-2-F 4.00% CGU-3-F 3.00% CCH-3CF₃ 7.00% CCH-5CF₃ 6.00% CWCU-3-F 12.00%

5.00%

Example M 10

CCP-2F.F.F 11.00% CCP-3F.F.F 10.00% CCP-5F.F.F 4.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CGU-2-F 3.00% CGU-3-F 3.00% CCH-3CF₃ 5.00% CCH-5CF₃ 5.00% CWCU-3-F 12.00% CECU-3-F 5.00% ECCP-2F.F.F 4.00% ECCP-3F.F.F 5.00% ECCP-5F.F.F 5.00%

5.00%

Example M 11

BCH-3F.F 10.80% γ₁ [mPa · s, 20° C.]: 145 BCH-5F.F 9.00% ECCP-30CF₃ 4.50% ECCP-50CF₃ 4.50% CBC-33F 1.80% CBC-53F 1.80% CBC-55F 1.80% PCH-6F 7.20% PCH-7F 5.40% CCP-20CF₃ 7.20% CCP-30CF₃ 10.80% CCP-40CF₃ 6.30% CCP-50CF₃ 9.90% PCH-5F 9.00% CWCU-3-F 10.02%

Example M 12

CCH-301 11.20% CCH-501 8.80% CCP-2F.F.F 8.00% CCP-3F.F.F 10.40% CCP-5F.F.F 4.00% CCZU-2-F 4.00% CCZU-3-F 13.60% CCZU-5-F 4.00% CH-33 2.40% CH-35 2.40% CH-43 2.40% CCPC-33 2.40% CCH-3CF₃ 6.40% CWCU-3-F 19.98%

Example M 13

CCH-3CF₃ 8.00% CCH-5CF₃ 7.00% CCP-2F.F.F 11.00% CCP-3F.F.F 12.00% CCP-5F.F.F 5.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CCP-20CF₃.F 7.00% CCP-30CF₃.F 3.00% CGU-2-F 4.00% CWCU-3-F 20.00%

Example M 14

CCH-301 14.00% CCH-501 16.00% CCP-2F.F.F 5.00% CCZU-2-F 4.00% CCZU-3-F 13.00% CCZU-5-F 4.00% CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 2.00% CCPC-35 3.00% CH-35 2.00% CH-43 2.00% CH-45 2.00% CCQU-2-F 5.00% CCQU-3-F 5.00% CWC-5-3 5.00%

5.00%

Example M 15

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 8.00% CCP-50CF₃.F 6.00% CGU-2-F 5.00% CGU-3-F 4.00% CCOC-3-3 2.00% CCOC-4-3 3.00% CC-5-V 7.00% CC-2-DDT 8.00% CC-3-DDT 8.00% CWCU-3-F 21.00%

Example M 16

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 9.00% CCP-50CF₃.F 7.00% CGU-2-F 7.00% CGU-3-F 3.00% CCOC-3-3 2.00% CCOC-4-3 2.00% CC-5-V 10.00% CWCU-3-F 18.00%

14.00%

Example M 17

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 6.00% CCP-30CF₃.F 6.00% CCP-50CF₃.F 6.00% CGU-2-F 10.00% CGU-3-F 10.00% CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 3.00% CC-3-OMT 3.00% CC-5-OMT 4.00% CWCU-3-F 17.00%

Example M 18

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 6.00% CCP-30CF₃.F 4.00% CCP-50CF₃.F 8.00% CGU-2-F 12.00% CGU-3-F 8.00% CCOC-3-3 3.00% CCOC-4-3 3.00% CCOC-3-5 3.00% CWCU-3-F 18.00% CC-2-DDT 3.00% CC-3-DDT 4.00%

Example M 19

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 9.00% CCP-50CF₃.F 9.00% CGU-2-F 10.00% CGU-3-F 11.00% CCOC-3-3 3.00% CCOC-4-3 3.00% CCOC-3-5 2.00% CWCU-3-F 18.00%

7.00%

Example M 20

CCP-2F.F.F 12.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 10.00% CCP-50CF₃.F 9.00% CGU-2-F 4.00% CGU-3-F 4.00% CCOC-3-3 2.00% CCOC-4-3 3.00% CCH-3CF₃ 8.00% CCH-5CF₃ 8.00% CCC-3-DDT 5.00% CWCU-3-F 18.00%

Example M 21

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 11.00% CCP-50CF₃.F 8.00% CGU-2-F 11.00% CGU-3-F 8.00% CC-5-V 10.00% CCC-3-DDT 5.00% CWCU-3-F 19.00%

Example M 22

PCH-5F 3.20% Δε [1 kHz, 20° C.]: +8.5 CCP-20CF₂.F.F 17.06% V₀ [V]: 1.34 CCP-30CF₂.F.F 16.02% CCP-50CF₂.F.F 17.06% CUP-2F.F 5.37% CUP-3F.F 5.37% CBC-33F 5.37% CBC-53F 5.37% CBC-55F 5.29% CWCU-3-F 19.91%

Example M 23

BCH-3F.F 10.47% Δn [589 nm, 20° C.]: +0.0933 BCH-5F.F 8.95% Δε [1 kHz, 20° C.]: +5.7 ECCP-30CF₃ 4.47% ECCP-50CF₃ 4.47% CBC-33F 1.79% CBC-53F 1.79% CBC-55F 1.79% PCH-6F 7.16% PCH-7F 5.37% CCP-20CF₃ 7.16% CCP-30CF₃ 10.74% CCP-40CF₃ 6.26% CCP-50CF₃ 9.84% PCH-5F 8.95% CWCU-3-F 10.51%

Example M 24

BCH-3F.F 10.81% BCH-5F.F 9.01% ECCP-30CF₃ 4.50% ECCP-50CF₃ 4.50% CBC-33F 1.80% CBC-53F 1.80% CBC-55F 1.80% PCH-6F 7.20% PCH-7F 5.40% CCP-20CF₃ 7.20% CCP-30CF₃ 10.81% CCP-40CF₃ 6.30% CCP-50CF₃ 9.91% PCH-5F 9.01% CWCU-3-F 9.95%

Example M 25

CCH-34 6.00% CC-5-V 6.00% CCH-3CF₃ 4.00% CCH-5CF₃ 7.50% CCP-2F.F.F 12.00% CCP-3F.F.F 10.00% CCP-5F.F.F 5.00% CCZU-2-F 5.00% CCZU-3-F 15.00% CCZU-5-F 6.00% CCP-20CF₃.F 8.50% CWCU-3-F 15.00%

Example M 26

CCH-35 5.00% CCOC-4-3 3.00% CCH-3CF₃ 8.00% CCH-5CF₃ 8.00% CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCZU-2-F 5.00% CCZU-3-F 15.00% CCZU-5-F 5.00% CCP-20CF₃.F 3.00% CWCU-3-F 20.00%

Example M 27

CCH-301 11.20% CCH-501 8.80% CCP-2F.F.F 8.00% CCP-3F.F.F 10.40% CCP-5F.F.F 4.00% CCZU-2-F 4.00% CCZU-3-F 13.60% CCZU-5-F 4.00% CH-33 2.40% CH-35 2.40% CH-43 2.40% CCPC-33 2.40% CCH-3CF₃ 6.40% CWCG-3-OT 20.00%

Example M 28

CCH-301 9.61% CCH-3CF₃ 5.49% CCH-501 7.55% CCP-2F.F.F 6.87% CCP-3F.F.F 8.93% CCP-5F.F.F 3.43% CCPC-33 2.06% CCZU-2-F 3.43% CCZU-3-F 11.67% CCZU-5-F 3.43% CH-33 2.06% CH-35 2.06% CH-43 2.06% CWCG-3-OT 31.34%

Example M 29

PCH-5F 3.22% CCP-20CF₂.F.F 17.17% CCP-30CF₂.F.F 16.12% CCP-50CF₂.F.F 17.17% CUP-2F.F 5.40% CUP-3F.F 5.40% CBC-33F 5.40% CBC-53F 5.40% CBC-55F 5.32% CWCG-3-OT 19.38%

Example M 30

BCH-3F.F 10.91% BCH-5F.F 9.09% ECCP-30CF₃ 4.55% ECCP-50CF₃ 4.55% CBC-33F 1.82% CBC-53F 1.82% CBC-55F 1.82% PCH-6F 7.27% PCH-7F 5.45% CCP-20CF₃ 7.27% CCP-30CF₃ 10.91% CCP-40CF₃ 6.36% CCP-50CF₃ 10.00% PCH-5F 9.09% CWCG-3-OT 9.09%

Example M 31

CCH-3CF₃ 8.00% CCH-5CF₃ 8.00% CCP-2F.F.F 11.00% CCP-3F.F.F 12.00% CCP-5F.F.F 5.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CCP-20CF₃.F 12.00% CCP-30CF₃-F 8.00% CCP-50CF₃.F 3.00% CWCG-3-OT 10.00%

Example M 32

CCH-301 4.00% Clearing point [° C.]: +87.0 CCH-501 5.00% Δn [589 nm, 20° C.]: +0.0678 CCP-2F.F.F 12.00% d · Δn [μm, 20° C.]: 0.50 CCP-3F.F.F 11.00% V₁₀ [V]: 1.46 CCP-5F.F.F 6.00% CCZU-2-F 5.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CGU-2-F 2.00% CGU-3-F 2.00% CCOC-3-3 3.00% CCOC-3-5 3.00% CCOC-4-3 4.00% CCH-3CF₃ 4.00% CCH-5CF₃ 5.00% CWCU-3-F 15.00%

Example M 33

CC-5-V 12.00% CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCZU-2-F 5.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CGU-2-F 2.00% CGU-3-F 2.00% CCOC-3-3 3.00% CCOC-3-5 2.00% CCOC-4-3 3.00% CCH-3CF₃ 4.00% CCH-5CF₃ 4.00% CWCU-3-F 16.00%

Example M 34

CCP-2F.F.F 13.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CWCU-3-F 18.00% CCP-20CF₃.F 9.00% CCP-30CF₃.F 5.00% CGU-2-F 5.00% CGU-3-F 4.00% CCOC-3-3 2.00% CCOC-4-3 3.00% CCOC-3-5 2.00% CC-5-V 7.00% CC-2-DDT 7.00% CC-3-DDT 8.00%

Example M 35

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CWCU-3-F 15.00% CCP-20CF₃ 5.00% CCP-30CF₃ 6.00% CCP-50CF₃ 6.00% CGU-2-F 10.00% CGU-3-F 9.00% CCOC-3-3 2.00% CCOC-4-3 3.00% CCOC-3-5 1.00% CC-5-V 3.00% CC-2-DDT 4.00% CC-3-DDT 8.00%

Example M 36

CCP-2F.F.F 13.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CWCU-3-F 18.00% CCP-20CF₃.F 8.00% CCP-30CF₃.F 7.00% CGU-2-F 6.00% CGU-3-F 4.00% CCOC-3-3 3.00% CCOC-4-3 3.00% CCOC-3-5 2.00% CC-5-V 6.00% CC-3-OMT 7.00% CC-5-OMT 6.00%

Example M 37

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CWCU-3-F 16.00% CCP-20CF₃ 7.00% CCP-30CF₃ 6.00% CCP-50CF₃ 6.00% CGU-2-F 9.00% CGU-3-F 11.00% CCOC-3-3 2.00% CCOC-4-3 2.00% CCOC-3-5 2.00% CC-3-OMT 6.00% CC-5-OMT 5.00%

Example M 38

CCP-2F.F.F 13.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CWCU-3-F 20.00% CCP-20CF₃.F 8.00% CCP-50CF₃.F 6.00% CGU-2-F 6.00% CGU-3-F 5.00% CCOC-3-3 2.00% CCOC-4-3 2.00% CC-5-V 10.00%

11.00%

Example M 39

CCP-2F.F.F 13.00% CCP-3.F.FF 11.00% CCP-5F.F.F 6.00% CWCU-3-F 25.00% CCP-20CF₃.F 7.00% CCP-50CF₃.F 3.00% CGU-2-F 6.00% CGU-3-F 4.00% CC-5-V 14.00% CCC-3-DDT 5.00% CCH-3CF₃ 3.00% CCH-5CF₃ 3.00%

Example M 40

CCH-301 9.45% CCH-3CF₃ 5.40% CCH-501 7.43% CCP-2F.F.F 6.75% CCP-3F.F.F 8.78% CCP-5F.F.F 3.38% CCPC-33 2.03% CCZU-2-F 3.38% CCZU-3-F 11.48% CCZU-5-F 3.38% CH-33 2.03% CH-35 2.03% CH-43 2.03% CWCU-3-F 32.50%

Example M 41

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 8.00% CCP-30CF₃.F 4.00% CCP-50CF₃.F 8.00% CGU-2-F 5.00% CGU-3-F 3.00% CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 3.00% CC-5-V 4.00% CWCU-3-F 20.00% CQU-2-F 5.00% CQU-3-F 5.00%

Example M 42

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃ 7.00% CCP-30CF₃ 6.00% CCP-50CF₃ 5.00% CGU-2-F 10.00% CGU-3-F 9.00% CCOC-3-3 3.00% CCOC-4-3 3.00% CCOC-3-5 2.00% CC-5-V 3.00% CWCU-3-F 18.00% CQU-3-F 3.00% CQU-5-F 3.00%

Example M 43

CCP-2F.F.F 11.00% CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCP-20CF₃.F 8.00% CCP-50CF₃.F 6.00% CGU-2-F 6.00% CGU-3-F 4.00% CCOC-3-3 3.00% CCOC-4-3 3.00% CCOC-3-5 3.00% CC-5-V 5.00% CC-3-OMT 8.00% CC-5-OMT 8.00% CWCU-3-F 18.00%

Example M 44

CCH-301 4.00% Clearing point [° C.]: 99 CCH-501 5.00% Δn [589 nm, 20° C.]: 0.0719 CCP-2F.F.F 12.00% V₁₀ [V]: 1.67 CCP-3F.F.F 11.00% CCP-5F.F.F 6.00% CCZU-2-F 5.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CGU-2-F 2.00% CGU-3-F 2.00% CCOC-3-3 3.00% CCOC-3-5 3.00% CCOC-4-3 4.00% CWCU-3-F 15.00% CCP-2F.F 4.00% CCP-3F.F 5.00%

Example M 45

CCH-301 14.00% Clearing point [° C.]: 98.0 CCH-501 16.00% Δn [589 nm, 20° C.]: +0.059 CCP-2F.F.F 5.00% Δε [1 KHz, 20° C.]: 4.7 CCZU-2-F 4.00% γ₁ [mPa · s, 20° C.]: 133 CCZU-3-F 13.00% CCZU-5-F 4.00% CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 2.00% CCPC-35 3.00% CH-35 2.00% CH-43 2.00% CH-45 2.00% CCQU-2-F 5.00% CCQU-3-F 5.00% CWC-5-3 5.00% CWCU-3-F 5.00%

6.00%

Example M 46

CCP-2F.F.F 13.00% Clearing point [° C.]: +86.5 CCP-3F.F.F 11.00% Δn [589 nm, 20° C.]: +0.0755 CCP-5F.F.F 6.00% VHR (5 min; 100° C.): 96.4% CCZU-2-F 4.00% V₁₀ [V]: 1.30 CCZU-3-F 16.00% CCZU-5-F 4.00% CCP-20CF₃.F 10.00% CCP-20CF₃ 2.00% CGU-3-F 3.00% CC-5-V 6.00% CCOC-4-3 2.00% CCWU-2-F 2.00% CCWU-3-F 6.00% CCWU-5-F 6.00%

Example M 47

CCP-2F.F.F 13.00% Clearing point [° C.]: +80.0 CCP-3F.F.F 11.00% Δn [589 nm, 20° C.]: +0.0809 CCP-5F.F.F 6.00% VHR (5 min; 100° C.): 98.8% CCP-20CF₃.F 6.00% V₁₀ [V]: 1.28 CCP-30CF₃.F 7.00% CCP-50CF₃.F 6.00% CGU-2-F 8.00% CGU-3-F 12.00% CCOC-5-3 2.00% CCOC-4-3 2.00% CCOC-3-5 2.00% CC-5-V 4.00% CCWU-2-F 7.00% CCWU-3-F 7.00% CCWU-5-F 7.00%

Example M 48

CCP-20CF₃ 6.00% Clearing point [° C.]: +80.5 CCP-30CF₃ 8.00% Δn [589 nm, 20° C.]: +0.0905 CCP-40CF₃ 8.00% Δε [1 KHz, 20° C.]: 10.7 CCP-50CF₃ 6.00% γ1 [mPa · s, 20° C.]: 154 CCP-20CF₃.F 12.00% CCP-2F.F.F 11.00% CCP-3F.F.F 13.00% CGU-2-F 10.00% CGU-3-F 10.00% CGU-5-F 9.00% CCWU-3-F 7.00%

Example M 49

CC-5-V 15.00% Clearing point [° C.]: +110.5 CCG-V-F 13.00% Δn [589 nm, 20° C.]: +0.0889 CCP-20CF₃.F 7.00% Δε [1 KHz, 20° C.]: 6.9 CCP-30CF₃.F 12.00% γ1 [mPa · s, 20° C.]: 164 CCP-20CF₃ 7.00% CCP-30CF₃ 7.00% CCP-40CF₃ 6.00% CCP-50CF₃ 7.00% CGU-3-F 8.50% CCGU-3-F 4.00% CBC-33F 2.50% CCWU-5-F 5.00% CCWU-3-F 6.00%

Example M 50

CC-5-V 15.00% Clearing point [° C.]: +109.9 CCG-V-F 15.00% Δn [589 nm, 20° C.]: +0.0884 CCP-20CF₃.F 9.00% Δε [1 KHz, 20° C.]: 6.8 CCP-30CF₃.F 12.00% γ1 [mPa · s, 20° C.]: 159 CCP-20CF₃ 7.00% CCP-30CF₃ 7.00% CCP-40CF₃ 6.00% CCP-50CF₃ 7.00% PGU-3-F 4.00% CCGU-3-F 4.00% CBC-33F 1.00% CCWU-5-F 7.00% CCWU-3-F 6.00%

Example M 51

CC-5-V 1.00% Clearing point [° C.]: +111.0 CCG-V-F 8.00% Δn [589 nm, 20° C.]: +0.0874 CCP-20CF₃.F 12.00% Δε [1 KHz, 20° C.]: 7.0 CCP-30CF₃.F 12.00% γ1 [mPa · s, 20° C.]: 180 CCP-20CF₃ 7.00% CCP-30CF₃ 7.00% CCP-40CF₃ 6.00% CCP-50CF₃ 7.00% BCH-32 3.50% PCH-7F 5.50% ECCP-3F.F 7.00% CCGU-3-F 4.00% CCWU-5-F 7.00% CCWU-3-F 7.00% CCWU-2-F 6.00% 

1. A liquid-crystalline medium containing a mixture of polar compounds of positive or negative dielectric anisotropy, said medium comprising one or more compounds of formula I

in which R¹ is an alkyl radical having from 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, where one or more CH₂ groups in these radicals may also, in each case independently of one another, be replaced by —O—, —S—,

—CH═CH—, —C═C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another,

L¹⁻⁶ are each, independently of one another, H or F, Z¹ and Z² are each, independently of one another, —CF₂CF₂— or a single bond, where Z¹≠Z², X is F, Cl, CN, OCN, NCS, SCN, an unsubstituted alkyl or alkoxy radical, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical having up to 6 carbon atoms, and u is 0 or 1, and v is 0 or 1, wherein


2. A medium according to claim 1, further comprising one or more additional compounds selected from formulae II, III, IV, V, VI, VII and VIII:

wherein R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms, X⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having from 1 to 6 carbon atoms, Z⁰ is —C₂H₄—, —CH₂O—, —OCH₂—, —COO—, —OCF₂—, —CF₂O—, —C₂F₄—, —CH₂CF₂— or —CF₂CH₂—, Y¹, Y², Y³ and Y⁴ are each, independently of one another, H or F, and r is 0 or
 1. 3. A medium according to claim 2, wherein the proportion of compounds of formulae I to VIII together in the mixture as a whole is at least 30% by weight.
 4. A medium according to claim 1, wherein the proportion of compounds of formula I in the mixture as a whole is from 1 to 50% by weight.
 5. A medium according to claim 2, wherein the proportion of compounds of formulae II to VIII in the mixture as a whole is from 20 to 80% by weight.
 6. A medium according to claim 1, wherein said medium further comprises one or more compounds of formula IVa

wherein R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms, X⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having from 1 to 6 carbon atoms, and Y² is H or F.
 7. A medium according to claim 2, wherein X⁰ is F, OCHF₂or OCF₃, and Y² is H or F.
 8. A medium according to claim 1, wherein R¹ is straight-chain alkyl.
 9. An electro-optical liquid-crystal display containing a liquid-crystalline medium according to claim
 1. 10. In a method of generating an electro-optical effect using an electro-optical display, the improvement wherein said display is according to claim
 9. 11. A medium according to claim 1, wherein said medium has a nematic phase down to −20° C., a clearing points above 80° C., a dielectric anisotropy value Δ∈ of ≧6, and a TN threshold voltage of below 2.0 V.
 12. A medium according to claim 1, wherein said medium has a nematic phase down to −40° C., a clearing points above 90° C., a dielectric anisotropy value Δ∈ of ≧8, and a TN threshold voltage of below 1.8 V.
 13. A medium according to claim 1, wherein said medium has a flow viscosity ν₂₀ at 20° C. of <60 mm²·s⁻¹, and a rotational viscosity γ₁ at 20° C. of <180 mPa·s.
 14. A medium according to claim 1, wherein said medium has a flow viscosity ν₂₀ at 20° C. of <50 mm²·s⁻¹, and a rotational viscosity γ₁ at 20° C. of <150 mPa·s.
 15. A medium according to claim 1, wherein said medium comprises one or more compounds of the following formulae:


16. A medium according to claim 1, wherein said X is F, Cl, CN, OCN, NCS, SCN, OCH₃, CH₃, OC₂H₅, C₂H₅, OC₃H₇, C₃H₇, CF₃, CF₂H, OCF₃, OCF₂H, OCFHCF₃, OCFHCH₂F, OCFHC₂HF, OCF₂CH₃, OCF₂CH₂F, OCF₂CHF₂, OCF₂CF₂CF₂H, OCF₂CF₂CH₂F, OCFHCF₂CF₃, OCFHCF₂CHF₂, OCFHCFHCF₃, OCH₂CF₂CF₃, OCF₂CF₂CF₃, OCF₂CFHCHF₂, OCF₂CH₂CHF₂, OCFHCF₂CHF₂, OCFHCFHCHF₂, OCFHCH₂CF₃, OCH₂CFHCF₃, OCH₂CF₂CHF₂, OCF₂CFHCH₃, OCF₂CH₂CHF₂, OCFHCF₂CH₃, OCFHCFHCHF₂, OCFHCH₂CF₃, OCH₂CF₂CHF₂, OCH₂CFHCHF₂, OCF₂CH₂CH₃, OCFHCFHCH₃, OCFHCH₂CHF₂, OCH₂CF₂CH₃, OCH₂CFHCHF₂, OCH₂CH₂CHF₂, OCHCH₂CH₃, OCH₂CFHCH₃, OCH₂CH₂CHF₂, OCCIFCF₃, OCCIFCCIF₂, OCCIFCHF₂, OCFHCCl₂F, OCClFCHF₂, OCClFCClF₂, OCF₂CHCl₂, OCF₂CHCl₂, OCF₂CCl₂F, OCF₂CClFH, OCF₂CClF₂, OCF₂CF₂CClF₂, OCF₂CF₂CCl₂F, OCClFCF₂CF₃, OCClFCF₂CHF₂, OCClFCF₂CClF₂, OCClFCFHCF₃, OCClFCClFCF₃, OCCl₂CF₂CF₃, OCClHCF₂CF₃, OCClFCF₂CF₃, OCClFCClFCF₃, OCF₂CClFCHF₂, OCF₂CF₂CCl₂F, OCF₂CCl₂CHF₂, OCF₂CH₂CClF₂, OCClFCF₂CFH₂, OCFHCF₂CCl₂F, OCClFCFHCHF₂, OCClFCClFCF₂H, OCFHCFHCClF₂, OCClFCH₂CF₃, OCFHCCl₂CF₃, OCCl₂CFHCF₃, OCH₂CClFCF₃, OCCl₂CF₂CF₂H, OCH₂CF₂CClF₂, OCF₂CClFCH₃, OCF₂CFHCCl₂H, OCF₂CCl₂CFH₂, OCF₂CH₂CCl₂F, OCClFCF₂CH₃, OCFHCF₂CCl₂H, OCClFCClFCHF₂, OCFHCFHCCl₂F, OCClFCH₂CF₃, OCFHCCl₂CF₃, OCCl₂CF₂CFH₂, OCH₂CF₂CCl₂F, OCCl₂CFHCF₂H, OCClHCClFCF₂H, OCF₂CClHCClH₂, OCF₂CH₂CCl₂H, OCClFCFHCH₃, OCF₂CClFCCl₂H, OCClFCH₂CFH₂, OCFHCCl₂CFH₂, OCCl₂CF₂CH₃, OCH₂CF₂CClH₂, OCCl₂CFHCFH₂, OCH₂CClFCFCl₂, OCH₂CH₂CF₂H, OCClHCClHCF₂H, OCH₂CCl₂CF₂H, OCClFCH₂CH₃, OCFHCH₂CCl₂H, OCClHCFHCClH₂, OCH₂CFHCCl₂H, OCCl₂CH₂CF₂H, OCH₂CCl₂CF₂H, CH═CF₂, OCH═CF₂, CF═CF₂, OCF═CF₂, CF═CHF, OCF═CHF, CH═CHF, OCH═CHF, CF₂CH₂CF₃, or CF₂CHFCF₃.
 17. A medium according to claim 1, wherein said X is F, Cl, CN, CF₃, CHF₂, OCF₃, OCHF₂, OCFHCF₃, OCFHCHF₂, OCFHCHF₂, OCF₂CH₃, OCF₂CHF₂, OCF₂CHF₂, OCF₂CF₂CHF₂, OCF₂CF₂CHF₂, OCFHCF₂CF₃, OCFHCF₂CHF₂, OCF₂CF₂CF₃, OCF₂CF₂CClF₂, OCClFCF₂CF₃, CH═CHF₂, OCH₃, OC₂H₅ or OC₃H₇.
 18. A medium according to claim 2, wherein said compound of the formula IV is


19. A medium according to claim 1, wherein said medium further comprises one or more dioxanes of formulae D1 to D4:

wherein R⁰ n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms.
 20. A medium according to claim 1, wherein said medium further comprises one or more compounds selected from formulae IX to XVIII:

wherein R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms, X⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having from 1 to 6 carbon atoms, and Y¹ and Y² are each, independently of one another, H or F.
 21. A medium according to claim 20, wherein X⁰ is F, Cl, CF₃, OCF₃ or OCHF₂, and R⁰ is alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 6 carbon atoms.
 22. A liquid-crystalline medium containing a mixture of polar compounds of positive or negative dielectric anisotropy, said medium comprising one or more compounds of formula I

in which R¹ is an alkyl radical having from 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, where one or more CH₂ groups in these radicals may also, in each case independently of one another, be replaced by —O—, —S—,

—CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another,

L¹⁻⁶ are each, independently of one another, H or F, Z¹ and Z² are each, independently of one another, —CF₂CF₂— or a single bond, where Z¹≠Z², X is F, Cl, CN, OCN, NCS, SCN, an unsubstituted alkyl or alkoxy radical, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical having up to 6 carbon atoms, and u is 0 or 1, and v is 0 or 1, wherein

and wherein said medium further comprises one or more compounds having fused rings of formulae A-1 to A-6:

wherein R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms.
 23. A medium according to claim 22, wherein said medium contains 3–15% by weight of compounds of formulae A-1 to A-6.
 24. A medium according to claim 2, wherein the proportion of compounds of formulae I to VIII together in the mixture as a whole is at least 30% by weight.
 25. A medium according to claim 1, wherein the proportion of compounds of formula in the mixture as a whole is from 1 to 50% by weight.
 26. A medium according to claim 2, wherein the proportion of compounds of formulae II to VIII in the mixture as a whole is from 20 to 80% by weight.
 27. A medium according to claim 25, wherein the proportion of compounds of formulae II to VIII in the mixture as a whole is from 20 to 80% by weight.
 28. A medium according to claim 1, wherein


29. A medium according to claim 2, wherein the medium comprises one or more compounds in which is straight-chain alkyl or alkenyl having from 2 to 7 carbon atoms.
 30. A medium according to claim 1, wherein the medium comprises one or more compounds of formula I in which R¹ is methyl, ethyl, n-C₃H₇, n-C₄H₉, n-C₅H₁₁ or n-C₆H₁₁.
 31. A medium according to claim 1, wherein the medium further comprises one or more compounds of formulae XIX to XXII:

wherein R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms, x⁰ is F, Cl, halogenated alkyl, alkenyl or alkoxy having from 1 to 6 carbon atoms, Y¹, Y², and Y³ are each, independently of one another, H or F, and the 1.4-phenylene rings are unsubstituted or substituted by methyl, CN, chlorine or fluorine.
 32. A medium according to claim 1, wherein the medium further comprises one or more compounds of formula XXIII

where

Z^(0′) is a single bond, —C₂H₄—, —C₄H₈—, —COO—, —O—CO—, —CF₂O— or —OCF₂, r⁰ is 1 or 2, R^(0′) is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms, and X^(0′) is OCF₃, F, Cl, CF₃, alkyl or alkoxy.
 33. A medium according to claim 32, wherein the proportion of the compounds of the formula XXIII in the medium is 5–40% by weight.
 34. A medium according to claim 1, wherein the voltage holding ratio is at least 96.4%.
 35. A medium according to claim 1, wherein said medium has a rotational viscosity γ₁ at 20° C. of <180 mPa·s.
 36. A medium according to claim 1, wherein said medium has a rotational viscosity γ₁ at 20° C. of <150 mPa·s.
 37. A medium according to claim 1, wherein said medium has a rotational viscosity γ₁ at 20° C of 130 mPa·s–180 mPa·s.
 38. A medium according to claim 34, wherein said medium has a rotational viscosity γ₁ at 20° C. of <180 mPa·s.
 39. A medium according to claim 34, wherein said medium has a rotational viscosity γ₁ at 20° C. of <150 mPa·s.
 40. A medium according to claim 34, wherein said medium has a rotational viscosity γ₁ at 20° C. of 130 mPa·s –180 mPa·s. 